The author of the Trojan refers to his or her work as "BlackHole RAT" and claims the malware is still in beta. Indeed, Sophos, who re-named the threat "OSX/MusMinim-A," says the current code is a very basic variation of darkComet, a well-known Remote Access Trojan (RAT) for Microsoft Windows. The source code for darkComet is freely available online.

The biggest threat from MusMinim appears to be its ability to display fake prompts to enter the system's administrative password. This allows the malware to collect sensitive user and password data for later use.

The Trojan also allows hackers to run shell commands, send URLs to the client to open a website, and force the Mac to shut down, restart or go to sleep arbitrarily. Other "symptoms" include mysterious text files on the user's desktop and full screen alerts that force the user to reboot.

Additionally, the malware threatens to grow stronger. "Im a very new Virus, under Development, so there will be much more functions when im finished," the author of the Trojan claims via its user interface.

Sophos believes the new malware indicates more hackers are taking notice of the increasingly popular Mac platform. "[MusMinim] could be indicative of more underground programmers taking note of Apple's increasing market share," says Sophos on its blog.

Another line from the malware's user interface supports the idea that hackers' interest in Mac OS X is growing. "I know, most people think Macs can't be infected, but look, you ARE Infected!"

In an apparent response to the increase in malware threats on the Mac, Apple is reportedly working with prominent information security analysts like Charlie Miller and Dino Dai Zovi to strengthen the overall security of Mac OS X Lion, the company's forthcoming major update to its desktop operating system. It's the first time Apple has openly invited researchers to scrutinize its software while still under development. Mac OS X Lion is scheduled to be released this summer.

In the meantime, Sophos tells Mac users to be cautious when installing software from less trustworthy sources. "Trojans like this are frequently distributed through pirated software downloads, torrent sites, or anywhere you may download an application expecting to need to install it," they say. Also, "patching is an important part of protection on all platforms" to prevent hackers from exploiting security vulnerabilities in web browsers, plug-ins and other applications.